Recent Studies of Hypernuclei Formation with Electron Beams at MAMI

transcript

Recent Studies of Hypernuclei Formationwith Electron Beams at MAMI

Patrick AchenbachU Mainz

Sept. 2o13

Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz

Theoretical calculationsCluster model, shell model, mean field…

Hypernuclear spectroscopy

Unique laboratory to investigate the YN interaction

Nuclear forceLarge base of NN

scattering data

Nuclear Structure

Normal / exotic nuclei

Hyperon forceLimited YN/YY scattering data

Nuclear StructureHypernuclei

Baryon interaction

The A = 4 isospin doublet

Nucleon-hyperon interaction can be studied by strange mirror pairs

Coulomb corrections are < 50 keV for the 4

ΛH - 4ΛHe pair

Energy differences of strange mirror pair are much larger than for 3H - 3He pair

With precise spectroscopy details of NY-interaction inferred

The A = 7 isospin triplet

Assumed CSB potential may be too naïve Further study on A = 4 hypernuclear systems necessary

[E. Hiyma, NPA 914, 130 (2013).]7Li(e,e’K+)7ΛHe

[N. Nakamura et al., PRL 110, 12502 (2013).]

7BeΛ(T=1)7LiΛ

Hypernuclear production methods

two regimes for hypernuclear and hyperfragment production:

- bound hypernuclear states- highly excited quasi-free region

hypernucleus quasi-free L[O. Hashimoto and H. Tamura, Prog. Part. Nucl. Phys. 57, 564 (2006).]

[From J-Lab Hall-A]

Hypernuclear decay-pion spectroscopy

fragmentation

two-body decay mono-energetic

Examples of - spectroscopy

KEK-E287, E326

beam: stopped K-

target: thick 7Li

7ΛLi 11

FINUDA Coll. and A. Gal, Phys Rev. B 681 (2009) 139

A. Gal, Nucl. Phys. A 828 (2009) 72

intense and high quality primary electron beam(R > 1014 Hz, < 100 mm)

+thin target (~10 mg/cm2)

decay π- spectroscopywith high resolutionand high accuracy

Severe limitations by statistics or momentum resolution

Goals of decay pion spectroscopy

• Masses with high accuracy for light hypernuclei:3LH, 4

LH, …, 11LB, 12

Determination of charge symmetry breaking (CSB) effects: (4

LH ↔ 4LHe), (6

LHe ↔ 6LLi), (7

LHe ↔ 7LLi* ↔ 7

LBe), …

• Search for hypernuclei near the neutron drip line:6LH, 7

LH, 8LH …

important information for L-S coupling [cf Hiyama]

6LH: the “superheavy hyper-hydrogen – puzzle” [cf Fukuda and Feliciello]

pion momentum resolution ~ 100 keV/c → mass resolution ~100 keV/c2 (FWMH) → accuracy of a few 10 keV/c2

Decay-pion spectroscopy at MAMI

Accessible hypernuclei

missing mass sepctroscopy

TOF system

tracking system

Cherenkov system

Particle detection system in KAOS

time-of-flight reso-lution with TOF walls

FWHM = 400 ps

pion detection ε > 95% by aerogel Cherenkov

Kaon identification using TOF system

protons

low / high momentum setting

• KAOS can cover 200–1300 MeV/c in only 2

settings

• clean kaon identification by TOF at low momenta

• Cherenkov information used for high momenta

low / high momentum setting

Pioneering experiment 2o11

• KAOS can be operated at zero-degree scattering angle

• PID suffers from high positron background

positrons

hadrons

Dedicated experiment 2o12

Decay pion detection

Decay pions from strange hadrons

(K,π)

(K,μ)(K,e)

(K,π)

(K,μ)(K,e)

Signal interpretation

Examples of decay-pion spectra

To minimize human bias two independent analyses performed:Final spectra to be released by end of year

Conclusions

- Two current questions in few-body physics:

- Decay pion spectroscopy gives access to ground-state masses of hypernuclei and could answer the questions!

- At MAMI pioneering experiments were followed by an experiment with a dedicated setup:

Clean tag on strangeness production at zero-degreeClean pion sample from weak decays of hyperons retrievedCurrent analysis limited by statistics → continuation with luminosity increase by one order of magnitude planned

How can we understand the A = 4 and A = 7 hypernuclei?Is the superheavy hyper-hydrogen nucleus bound?

A1 Hypernuclear Collaboration

Recent Studies of Hypernuclei Formation with Electron Beams at MAMI

Documents